1. Field of the Invention
The present invention relates in general to computers, and more particularly to a system and method of determining whether a volume table of contents (VTOC) is valid prior to withdrawing the volume in a fast replication relationship.
2. Description of the Prior Art
Data processing systems often work with large amounts of data and require mechanisms to manage the storage and archiving of that data. For example, transaction processing systems typically access large databases and log results such as transaction records at a very high rate. The ability to quickly and reliably copy data from one storage area to another enables the deployment of efficient and reliable high-performance processing applications and systems.
In addition to increased performance, fast replication capable systems simplify the code complexity of I/O intensive processes such as those conducted on large mainframe systems and the like. System performance may also be increased in that support for fast replication operations may be provided by low-level drivers and devices that are optimized for performance.
Fast replication capable systems preferably support multiple concurrent fast replication data transfers. Since the data transfer may be deferred indefinitely, the act of initiating a fast replication operation between a source and a target volume is often referred to as “establishing a fast replication relationship.” Likewise, canceling a pending fast replication transfer may be referred to as “withdrawing a fast replication relationship.”
Without support for fast replication relationships, conducting a point-in-time copy often requires that a system suspend all tasks that access a source and/or target device. Since many systems do not have explicit knowledge of the devices that will be accessed by each task, those systems require suspension of all tasks except for the task conducting the actual fast replication operations. Suspension of the various tasks or processes in order to conduct fast replication operations greatly reduces the performance of multi-tasking systems.
One challenge of fast replication capable systems concerns the integrity of the volume table of contents (VTOC) when a volume is withdrawn from a fast replication relationship. The possibility exists that, upon a withdrawal, either on an intentional or inadvertent basis, the VTOC contains invalid data. The VTOC can contain invalid data if, at the time data was being physically written to the VTOC using a fast replication method, the volume was withdrawn and the method was terminated midstream. Such an intentional or inadvertent withdrawal can be detrimental to applications or programs that later attempt to use this volume.